Anodic Dissolution Behavior of the Crack Tip of X70 Pipeline Steel in Near-Neutral pH Environment

In this work, the anodic dissolution behavior of the fresh metal surface at crack tip of X70 steel in near-neutral pH environment was investigated using galvanic corrosion simulation method. The solution environment, strain, strain rate, hydrogen enrichment, and fresh metal surface at the crack tip were considered. Corrosion current of the specimen during fast stretching increased linearly with plastic strain. The increment and increase rate of the corrosion current during plastic deformation stage were dependent on the strain rate. Combining Faraday's law and crack tip strain rate equation, the crack growth rate (CGR) induced by the anodic dissolution of the fresh metal surface was calculated. Results show that CGR caused by anodic dissolution was roughly one order lower than that measured on the compact tensile specimen under cyclic load. This finding indicated that hydrogen embrittlement may play a dominate role in stress corrosion crack propagation of pipeline steels in near-neutral pH environment.

在这项工作中，采用电偶腐蚀模拟方法研究了X70钢裂纹尖端新鲜金属表面在近中性pH环境中的阳极溶解行为。考虑了溶液环境、应变、应变速率、氢富集以及裂纹尖端的新鲜金属表面等因素。试样在快速拉伸过程中的腐蚀电流随塑性应变呈线性增加。塑性变形阶段腐蚀电流的增量和增长率取决于应变速率。结合法拉第定律和裂纹尖端应变速率方程，计算了新鲜金属表面阳极溶解引起的裂纹扩展速率（CGR）。结果表明，阳极溶解引起的裂纹扩展速率比循环载荷下紧凑拉伸试样所测得的速率大约低一个数量级。这一发现表明，氢脆可能在近中性pH环境下管线钢的应力腐蚀裂纹扩展中起主导作用。